Foundry sand binder with easy breakdown - prepd. from sodium silicate binder with sugar and water soluble oxidant

摘要

An aq. liq. binder for foundry moulding sands contg. an alkali metal silicate with a compatible water-soluble oxidant where 10-40 wt.% of the liq. is an oxidisable org. material which is only oxidised at higher temp. i.e. not at room temp. The materials are sodium silicate with wt. ratio SiO2:Na2O between 2.0 and 3.3; a mixt. or sodium chlorate and sodium dichromate as oxidant; and saccharose as the org. matl. The pref. liq. has 60-75 wt.% sodium silicate soln (Twaddell 84-120 degrees); 15-30 wt.% org. matl; 1-15 wt.% oxidant (with wt less than half the wt. of the organic material); and 0-20 wt.% water. Other suitable oxidants are the nitrates chromates, permanganates or chlorates of an alkali metal, and other org. materials are e.g. starch, dextrin, cellulose or sugar. The pref. amt. of binder is 2-8 wt.% of the moulding sand, and the materials may be added separately as suspensions or dispersions. The moulds may be thermaly hardened at 160-200 degrees C or by a combination of heat and CO2.